Exploring Exotic Nuclear Shapes at High Angular Momentum at ATLAS

D. J. Hartley ATLAS Users Workshop 2014

A Common Theme

New experimental capabilities by combining Digital Gammasphere (DGS) with CARIBU and other devices (plunger, Phoswich Wall, LaBr3) will allow for the investigation of exciting nuclear structure phenomena

γ = 0˚γ = 60˚

Pot. Energy Surfaces

PROLATE

OBLATEγ ~ 25˚TRIAXIAL

Deformation ε 2

Search for Stable Triaxial Deformation

γ = 0˚γ = 60˚

Pot. Energy Surfaces

PROLATE

OBLATEγ ~ 25˚TRIAXIAL

Deformation ε 2

Search for Stable Triaxial Deformation

Robust triaxial shapes have been sought after for decades!

“The study of rotational motion in nuclei with asymmetric shapes is potentially a field of broad scope.” Bohr and Mottelson Vol. 2 pg. 176,

It is only in this last decade that triaxial strongly deformed shapes have been observed. (eg. wobbling modes in Lu nuclei and now the ultra-high spin Er results.)

Triaxiality and Shape Co-existence in N-rich Zr/Mo/Ru Region

• Theory suggests triaxial shapes along with prolate/oblate shape competition

• Recent lifetime analysis suggests even-even nuclei may be prolate, γ-soft rotors

• Exploration needed in the odd-A systems and to search for evidence of triaxiality

Washington Univ., ANL, Milano, Krakow, Notre Dame, Mississippi State Univ., LBNL

8/26/13 WR, DGS 66

Qt(I) dataFull symbols: this workOpen symbols: literaturecircles = gsb, triangles = band

Downslope with spin:Suggests 0° (prolate) > 0°Rules out oblate, near-oblate shapes(Same conclusions from (1) data)

Theoretical calculations“Cranked relativistic Hartree-Bogoliubov”

Green, dashed: prolateRed, full: oblate, near oblate104Mo can be best described by theory

Snyder et al., Physics Letters B 723, 61 (2013)

Future Plans

• Odd-A nuclei may be better triaxial candidates• Accepted experiment on 105,106Nb (CARIBU + GS

+ Phoswich Wall) – Milano, Krakow, ANL, & Washington

• Proposing another Cf source experiment to perform lifetime analysis - Washington– Plunger + Phoswich Wall + GS

• Neutron-rich nuclei in the Mo/Ru are predicted to be triaxial in or near their ground states

• Is wobbling observed at low spins in even-even nuclei?

• Coulex CARIBU beams with GS or Gretina

• Need to use arrays with CHICO2

Wobbling in Neutron-Rich Nuclei?Notre Dame,

Mississippi St. Univ., LBNL

S.J. Zhu et al., Int. J. Mod. Phys. E 18, 1717 (2009)

Characteristics of Triaxial Ultrahigh-Spin Bands Near N=90

• Experimentally measure spin (none are currently known)

• Determine quadrupole moments

• Determine configurations for structures

Florida State, US Naval Academy, Liverpool, Daresbury

158Er

Recent Theoretical Interest

73 162Ta 163Ta 164Ta 165Ta 166Ta 167Ta 168Ta 169Ta

72 161Hf 162Hf 163Hf 164Hf 165Hf 166Hf 167Hf 168Hf

71 160Lu 161Lu?

162Lu 163Lu 164Lu 165Lu 166Lu 167Lu

70 159Yb 160Yb 161Yb 162Yb 163Yb 164Yb 165Yb 166Yb

69 158Tm 159Tm 160Tm 161Tm 162Tm 163Tm 164Tm 165Tm

68 157Er 158Er 159Er 160Er 161Er 162Er 163Er 164Er

67 156Ho 157Ho 158Ho 159Ho 160Ho 161Ho 162Ho 163Ho

Z N

89 90 91 92 93 94 95 96

Ultra high-spin TSD Wobbling TSD

Find Both UHS and Wobbler in Same Nucleus (161Lu)

• Clearly UHS and Wobbling bands are different structures

• However, since they are both strongly deformed and based on triaxial shapes the UHS may feed strongly into a low-spin Wobbling structure if both are found in the same nucleus

Future UHS/Wobbling Experiments

• Measure relative quadrupole moment of UHS band and Wobbling structure of 161Lu

• Measure quadrupole moments of other UHS bands to understand underlying structure similar to A~150 nuclei

• Wobbling in UHS Minimum?• DGS is a must to do these in a reasonable time

Measuring the Evolution of Shapes Through Lifetime Measurements

• Use plunger with stable ATLAS beams and CARIBU beams

• Combine GS or X-array with LaBr3 array to measure lifetimes

Darmstadt/Yale

• Plunger for Reaccelerated RIB Beams• Will fit into GS or GRETINA• Couple with CHICHO2, Phoswhich

Wall, etc.

15Volker Werner | TU Darmstadt,

AG Pietralla | ATLAS User Workshop | May 2014

Better Understanding of Nuclear Shape Evolution

QT (J)/Q

T (2)

170Hf

Standard RDDS Plunger Experiments

Centrifugal Stretching

Search for new shape/phase-transitional regions, e.g., p-rich Ce/Nd/Sm isotopes

Needs ATLAS,GammaSphere

M. Smith, V. Werner, et al.,PRC87, 044317 (2013)

Probe specific nucleiFor a new benchmark:Partial DynamicalSymmetriesFor example:Certain states (e.g., GSB)exhibit part of a (dynamical)symmetry (SU(3), O(6), ...)

-> see work by Leviatan, van Isacker, Pietralla, Casten, ....

Darmstadt/Yale

Volker Werner | TU Darmstadt, AG Pietralla | ATLAS User Workshop | May 2014

16

What's going on at N=98? Fast Timing with LaBr3 & GS

176W : J.-M. Regis et al. NIM A 606 (2009)172W, 178W : M. Rudigier et al. Nucl. Phys. A 847 (2010)

(measured with LaBr3)

Fast Timing Experiments using electron spectroscopy and/or LaBr3 reveal peculiarity

Needs ATLAS Stable Beam

?

Testing Advanced Shell Model Calculations in the A=80 Region

• New shell model calculations are now available to describe mass 80 nuclei

• Explore structures in this evolving region

• Start with 83Mo

“Borrowed” from Witek Nazarewicz

Florida State University

Further Into the Future…

GRETA

Extra Slides

8/26/13 WR, DGS 2121

Angle: < Fission Axis, Gammasphere ring

Strength 230 μCi

Arrangement Pt backing (440 mg/cm2), Au leaf

HERCULES Fragment ToF and pulse height, fission-axis direction

Gammasphere ToF start time, γ-ray energy and time

Running time 18 d

# Correlations 2.1 × 109 (fragment-γ4)

252Cf Source Experiment*10+

1

Red: analyzed, blue: contaminant peaks

Snyder et al., Physics Letters B 723, 61 (2013)

* Using the infrastructure at ATLAS

Bohr & Mottelson Vol. II, p. 176

Ultrahigh-spin bands in 157,158Er- E.S. Paul et al., PRL 98, 012501 (2007)

A.V. Afanasjev, Yue, Shi, and W. Nazarewicz, PRC 86, 031304(R) (2012)

Measure Spin of Ultrahigh-Spin TSD Bands USNA, Florida St. Univ., Liverpool, Daresbury

Volker Werner | TU Darmstadt, AG Pietralla | ATLAS User Workshop | May 2014

24

New Reaccelerated RIB Plunger Underway

Developed by Yale (VW) and Cologne, Si Disk to be purchased by TU Darmstadt

Will fit into GammaSphere, GRETINA, MiniBall, AGATA, ...Will be able to couple to other auxiliaries like CHICO2, PhoSwitch Wall

Roadmap for Theory of Nuclei

Overarching goal:

To arrive at a comprehensive microscopic description of all nuclei and low-energy reactions from the the basic interactions between the constituent nucleons

...provides the guidance

Nazarewicz